Susan Sontag's seminal essay On Photography famously asserted that "To collect photographs is to collect the world." Yet within the world of collecting, photography is too often set apart from other forms of art.

The existence of the newly conjoined photo fairs, Photo-London and Paris Photo, raises an interesting question - is photography being spotlighted or ghettoized?

Photo fairs seem to be attempting some kind of affirmative action programme for the medium, but why would photography need special treatment when all-important indicators otherwise show that it is well assimilated in the contemporary art scene?

Almost every well-regarded contemporary art gallery now includes a few photographers among their roster. Photography is also increasingly asserting itself on the auction block as an important investment. And its prices in the galleries and at the major fairs reflect its serious status. Yet collecting photography remains a more complicated and fraught endeavour than collecting painting or even sculpture.

The unique issues around collecting photography initially arise from the medium's reproducibility. On the surface, collectors concerned with diminishing the value of their investment seem wise to stick with unique objects and shy away from mediums that can be made in multiples. But photography is not alone in being vulnerable to the dangers of mass reproduction. As Steve Pulimood reported in his article on Larry Gagosian's plans for posthumous reproductions of Giacometti sculptures, "From Rodin to Picasso, the rampant abuse of artist's moulds has flooded the market with fakes." Still, sculpture is understood to be precious while many collectors still remain wary of photography.

The showcasing of photography at this year's Affordable Art Fair demonstrates an interesting reason for photography's identity crisis. The medium may be seen as too demographic to appeal to many collectors. Situated at the entrance to the main fair, the organisers of AAF Photo2007 explicitly positioned photography as an accessible gateway to potential casual or first-time collectors.

Almost none of the work at the Affordable Art Fair was striking, except for the rock'n'roll photographs on show at the Birmingham-based Snap Gallery's booth. There, you could buy a beautiful signed and numbered print by Don Hunstein for £1,850 (everything at the fair was priced between £50 and £3,000). The image was from an edition of 50, and showed Bob Dylan and his then-girlfriend Suze Rotolo as a cute cool couple walking together down the street in downtown New York.

It is the same shot that was on the cover of The Freewheelin' Bob Dylan, and it is arresting that such an iconic image would sell for so little or be seen in a context where the other art being sold might be of personal, but never historic, importance.

It is hard to think of a painted portrait with such wide-reaching appeal yet so much intimacy as Hunstein's Dylan. In this instance, photography's democratic potential works against it. Where the image is so ubiquitous, why not just hang the CD jacket on your wall? It seems almost redundant to purchase it as itself.

In contrast, the photographers who should and do gain the most critical recognition, and garner the most success at the highest levels of the art world, are those who make looking at a photograph in person into an experience that is never capable of being transmitted through the image's reproduction on a printed page or online.

Artists like Andreas Gursky, Jeff Wall and Ryan McGinley create prints whose clarity of colour, scale and emotion are so intense that any poster, online or magazine reproduction looks flat and dull in comparison.